A camera system of the type used with the present invention includes a camera and at least one remote device, usually a supplemental flash unit. The camera system is designed to control the operation of the remote device when a source device of the camera sends a signal that is detected by the remote device. On many cameras, the source device is part of a camera flash unit that mounts to a hot-shoe of the camera. A signal can be sent from the source device to the remote device via wires, cables, pulses of light, or other common method for transmitting a signal that carries a data stream. Sometimes, an existing camera system's method for transmitting a signal is not adequate or reliable because of inherent drawbacks of the camera system.
Few camera manufacturers have opted to sell camera systems that use a radio transmission to send a signal from the source device to the remote device. Many photographers prefer a radio transmission because there are no wires or cables, and because there are failure concerns when using an infrared signal if there is too much ambient light, inadequate surfaces for reflecting light, or it is just difficult to negotiate a line of sight between the source device and the remote device. Physical obstacles and direct sunlight are not a concern when just using a radio transmission. Unfortunately, possibly due to differing government regulation of radio transmissions from country to country, the most popular camera systems transmit a signal using infrared light pulses rather than radio waves. Canon U.S.A. Inc. provides one of the most sophisticated systems, Canon's E-TTL (Evaluative Through-The-Lens) flash exposure control. Details about the structure and meaning of some of Canon's IR signals are presented in U.S. Pat. Nos. 6,404,987 and 6,831,420.
One popular solution to providing a radio operated camera system to professional photographers is to transmit a radio signal when certain camera settings are detected, such as an open shutter, and to receive a trigger instruction at the remote device that can be used to operate a flash. The problem with this solution is that the camera is not able to communicate any control instructions that are normally sent via the IR signal before the trigger instructions. To prevent the loss of these control instructions, a camera system designed to use a radio transmission would most likely use some sort of preamble signal that could modulate and otherwise prepare a transmitter and receiver just prior to the transmission of all of the information contained in an existing camera's IR signal.
Without a preamble signal, or some other way of knowing that an IR signal is about to be sent, there is no system currently available that is capable of detecting and processing an IR signal sent by a source device, establishing a radio bridge, and then retransmitting to a remote device quickly enough to support the ability of a camera system to use flash at high shutter speeds (a high speed sync). Every light pulse sent by an infrared type source device carries important information that is either part of control instructions or part of trigger instructions. There is simply no time for a radio bridge to process and determine whether a pulse train is from the environment or from the source device. The drawback of any currently available radio bridge system is the loss of the control instructions that precede the trigger instructions in a data stream normally sent by the source device to the remote device. Without having first relayed current control instructions, a trigger instruction based on a camera's shutter simply causes the remote device to flash based on manual settings of the remote device.